The subject of the present invention is a bituminous product and a process for preparing it.
The term xe2x80x9cbituminous productxe2x80x9d is understood to mean bitumens or any bitumen-based composition.
Bituminous products are used in particular in the fields of roadways, roofing materials, coverings and membranes. The use of asphalt for producing roadways may also be mentioned.
In general, bituminous products include aggregates or fillers. These may be granulates or stones, sand and fines.
However, such products have many drawbacks when they are used as such for various applications: mention may be made in particular of a high temperature sensitivity, limited adhesion to aggregates, mediocre low-temperature properties and low fatigue and impact strength.
In addition, bituminous products are difficult to handle and require specific technologies.
Thus, in the case of a roadway, in particular in the case of the pavement of a road, the principal constituents are bituminous mixes that consist of 95% by weight of aggregates and 5% by weight of bitumen, which serves as binder. In this case, the role of the bitumen as binder is predominant with regard to the properties of the road, which is subjected to various stresses of a mechanical origin, namely thermal fracture, fatigue and rutting.
This is because at low temperature (below about xe2x88x9210xc2x0 C.), the binder, i.e. the bitumen, is in a glassy state and becomes brittle. Long transverse cracks due to the thermal stresses (thermal fractures), which are microcracks because of the heterogeneity of the material, may then form.
At a higher temperature (about at least 0xc2x0 C.), the pavement may still crack owing to the effect of fatigue. This results in a multitude of cracks that are principally longitudinal and interconnected.
Finally, at higher temperatures (about 60xc2x0 C.), the bitumen passes from the solid state to the viscous state, becoming more and more fluid. Thus the repeated passage of heavy loads, that vehicles, including heavy goods lorries, constitute, on the pavement contribute to making the bitumen, and therefore the pavement, undergo permanent deformation. This phenomenon is the origin of rutting.
The binder also makes the pavement impermeable, thus protecting the base courses of the road.
The main features required of the pavement of a road and therefore of the bituminous products serving as binder are therefore:
good crack resistance at low temperature (typically xe2x88x9215xc2x0 C.);
low deformation at high temperature (typically +60xc2x0 C.); and
good fatigue strength in order to improve durability.
Manufacturers generally use additives to palliate the shortcomings of bituminous products and thus improve their properties.
It is known in particular to add phosphoric acids or polyphosphoric acids to these bituminous products.
However, these acids are not easy to use since these products are highly viscous and therefore not able to be handled easily. It follows that there are not insignificant losses of product, which incur higher costs.
In addition, these acids may crystallize during their storage and they are no longer usable as such, unless they undergo a heat treatment, which involves further handling and an increase in the costs due to the heat treatment step.
To meet the requirements of manufacturers, it has become necessary to find additives which palliate the drawbacks of phosphoric acids or polyphosphoric acids.
Thus, the problem that the present invention aims to solve is to provide an additive for bituminous products that can be handled easily, compared with phosphoric acids or polyphosphoric acids.
For this purpose, the invention provides a process for preparing a bituminous product, characterized in that a compound based on a phosphoric or polyphosphoric acid supported on a mineral oxide of high porosity is used.
The invention also provides a bituminous product that can be obtained by the process described above.
The advantage of the compound based on a phosphoric or polyphosphoric acid supported on a mineral oxide of high porosity is that it is in the form of a powder and can therefore be handled very easily compared with the abovementioned acid solutions, which are highly viscous.
Another advantage of this compound is that it makes it possible to reinforce the bituminous products into which it is incorporated, in particular as regards high-temperature strength.
Finally, this compound retains the same properties as those of phosphoric or polyphosphoric acids.
Other advantages and features of the present invention will become clearly apparent on reading the description and the examples, given solely by way of illustration but implying no limitation, that follow.
The invention firstly relates to a process for preparing a bituminous product, characterized in that a compound based on a phosphoric or polyphosphoric acid supported on a mineral oxide of high porosity is used.
The compound used according to the invention comprises a mineral oxide.
The mineral oxide must be of high porosity, which means that its pore volume is at least 1 ml/g and preferably at least 3 ml/g.
The mineral oxide may also have a large surface area.
The mineral oxide of high porosity may be especially chosen from silicas, aluminas and aluminosilicates.
Preferably the mineral oxide is a silica. Preferably said silica is a precipitated silica. For example, it may be a TIXOSIL 38, TIXOSIL 38D, TIXOSIL 38X or TIXOSIL 365 silica from Rhodia.
The mineral oxide may also be lamellar or exfoliated.
The mineral oxide may also be obtained from an oxide precursor.
The compound used according to the invention also comprises a phosphoric or polyphosphoric acid.
Preferably, the phosphoric acid is orthophosphoric acid.
Orthophosphoric acid, also called monophosphoric acid, corresponds to H3PO4.
The polyphosphoric acids according to the invention may be chosen from those described in the book entitled xe2x80x9cPhosphorus an outline of its Chemistry, Biochemistry and Usesxe2x80x9d, 5th Edition, D. E. C. Corbridge, Elsevier, 1995, pages 170 and 180 to 182.
The polyphosphoric acid is preferably chosen from pyrophosphoric acid or diphosphoric acid of formula H4P2O7, triphosphoric acid of formula H5P3O10, polyphosphoric acids of formula Hn+2PnO3n+1, metaphosphoric acids of formula HnPnO3n or a blend thereof.
As indicated on page 181 of the abovementioned document xe2x80x9cPhosphorus an outline of its Chemistry, Biochemistry and Usesxe2x80x9d, commercial phosphoric acid or polyphosphoric acids are characterized by their P2O5 or H3PO4 equivalent expressed as a percentage by weight.
Thus, there is a class of acids called superphosphoric acids whose H3PO4 equivalent is greater than 100. These superphosphoric acids are the preferred polyphosphoric acids.
The compound employed according to the invention may be produced by bringing the mineral oxide into contact with phosphoric or polyphosphoric acid.
The maximum amount of phosphoric or polyphosphoric acid employed corresponds to the maximum amount of the said acid that can be absorbed by the mineral oxide.
The compound employed according to the invention may be produced by a process which includes a drying step after the mineral oxide has been brought into contact with the phosphoric or polyphosphoric acid.
In addition, the compound employed according to the invention may be hydrophobicized. In this case, it will be preferred to use hydrophobic agents chosen from silicones and fatty acids.
Several methods of implementing the incorporation of the compound according to the invention into the bitumen composition are possible.
Among these, one method of implementation relates to a process comprising the following steps:
1xe2x80x94the bitumen composition is heated to a temperature of between 120 and 190xc2x0 C.; and
2xe2x80x94a sufficient amount of compound according to the invention is added, with stirring, to the bitumen composition of step 1.
The invention then relates to a bituminous product that can be obtained by the process described above.
The bituminous product according to the invention may be prepared according to a process for preparing hot mixes, which employs the compound according to the invention.
This hot-mix process comprising an additional step to the above process. This step consists in adding, with stirring and at a temperature of between 120 and 190xc2x0 C., aggregates to the bitumen composition before, during, simultaneously with, or after the addition of compounds according to the invention.
For example, this hot-mix process may comprise the following steps:
1xe2x80x94the bitumen composition is heated to a temperature between 120 and 190xc2x0 C.;
2xe2x80x94a sufficient amount of compound according to the invention is added, with stirring, to the bitumen composition of step 1; and
3xe2x80x94aggregates are added, with stirring, to the bitumen composition of step 2.
In general, the aggregates are preheated to a temperature greater than 120xc2x0 C., and generally between 120 and 190xc2x0 C.
The invention also relates to the bituminous product that can be obtained by the hot-mix process described above.
The bituminous product according to the invention may also be prepared according to a process for preparing cold mixes, which employs the compound according to the invention.
This second possible method of implementation for incorporating the compound according to the invention is carried out at room temperature.
This process comprises the following steps:
1xe2x80x94a bitumen emulsion is prepared by mixing water, bitumen and an emulsifier at room temperature;
2xe2x80x94a sufficient amount of compound according to the invention is incorporated into a bitumen emulsion with stirring at room temperature;
3xe2x80x94the emulsion obtained in step 2 is spread in order to obtain a uniform layer of the mixture obtained in step 2; and
4xe2x80x94the bitumen emulsion is broken.
The invention also relates to the bituminous product that can be obtained by the cold-mix process described above.
It is also possible to add aggregates to the bitumen composition, with stirring and at room temperature, after the addition of compound according to the invention in step 2.
Finally, a third method of implementation is also possible which combines the above two, xe2x80x9chotxe2x80x9d and xe2x80x9ccoldxe2x80x9d, methods of implementation.
This process comprises the following steps:
1xe2x80x94the bitumen composition is heated to a temperature between 120 and 190xc2x0 C.;
2xe2x80x94a sufficient amount of compound according to the invention is added to the bitumen composition of step 1 with stirring;
3xe2x80x94an emulsion of the bitumen obtained in step 2 is prepared by mixing water, the said bitumen and an emulsifier;
4xe2x80x94the emulsion obtained in step 3 is spread in order to obtain a uniform layer of the mixture obtained in step 3; and
5xe2x80x94the bitumen emulsion is broken.
This process may include an additional step which consists in adding, with stirring and at room temperature, aggregates to the bitumen emulsion obtained in step 3 of the process.
It should be noted that examples of bitumens to which the compound according to the present invention may be added include natural bitumens, pyrobitumens and artificial bitumens. Bitumens that are particularly preferred are those used for roadways, such as asphalt or maltha. Even more preferably, asphalt is used.
The bituminous product according to the invention may also contain other additives normally used in the bitumen field.
Mention may also be made as suitable additives according to the invention of elastomers, plastomers, or any other chemical agent known to those skilled in the art for improving the physico-chemical properties and the debonding resistance, whether by themselves or as blends.
The emulsifiers used to emulsify the bitumen are emulsifiers that are normally used by those skilled in the art in this technical field.
Provision may also be made for the bitumen used to be preoxidized hot by contact with air.
Finally, the invention relates to the use of the bituminous product according to the invention for the manufacture of mortars, coverings, especially road treatments.
The following examples illustrate the invention without however limiting the scope thereof.